Transcript G080230-00 - DCC

Status of the advanced LIGO laser
O. Puncken, L. Winkelmann, C. Veltkamp,
B. Schulz, S. Wagner, P. Weßels, M. Frede, D. Kracht
Content
• Setup
• Status in October 2007
• Current status
• Characterization work
– Crystals
– Mirrors
– Diodes
• System improvement / outlook
– Crystal cooling
Advanced LIGO PSL: high power laser
high
power
stage
medium
power
stage
premodecleaner
to
interferometer
NPRO
reference
cavity
AOM
Setup
Setup
Adv. LIGO electronics
Start-up behavior
200
180
160
140
oszillator at
working point
(one direction + amplifier,
not locking )
160
140
120
output power (W)
output power (W)
180
100
80
60
120
starting
oszillator
100
80
locked system
starting
amplifier
60
40
st
20
1 stability range
40
0
0
50
100
20
150
200
250
3500
4000
time (s)
0
0
500
1000
1500
2000
2500
3000
time (s)
Complete system started and locked after 3 min !
status 10/07
Beam quality
• Output power: 180.5 W
• 91.5% (~165 W) in TEM00
status 10/07
53h test run
200
24
180
23
140
120
22
100
80
21
60
40
0
20
Relock events
20
0
10
20
30
40
Temperature [°C]
Output Power [W]
160
50
19
Time [h]
status 10/07
Current status
• ≈ 174 W at 4 x 185 W
pump power
• 91 % in TEM00
• DC noise ≈ 5% (not
changed)
• Typical relock time
< 50 ms (not
changed)
• Startup:
complete system
started after 3 min
Doping of the crystals
• Nd:YAG crystals, 40mm 0.1 at % doped
region / 7mm undoped endcap
– Doping specifications 0.1 at. % +/- 0.01 at. %
• Actual incoming from different vendors:
– ~ 0.1 – 0.13 at %
– Doping gradient over crystal length
•  different thermal optical effects !
Integrated fluorescence
Integrated fluorescence
Spot diameters from integrated
fluorescence
 Crystals are slightly different doped
 Characterization of the incoming crystals
Incoming inspection of the components
• Since small qualitative differences seem to
have a big effect, this is the only way to
guarantee the reproducibility of the system !
• Development of characterization facilities for
– Crystals
– Mirrors and lenses
– Pump diodes
Crystal characterization
•
•


so far: longitudinal measurement of the fluorescence
upcoming: transversal measurement of the absorption
Direct measurement of the doping concentration
Possibility of „scanning“ the crystal to find doping
gradients
Mirror characterisation
automated polarimeter
polarization analysis software
NPRO
/4 /2
PBS
/4
PBS
PD2
PD1
Diode characterisation
• Automated test
facility for measuring
– Slope
– Spectral FWHM at
different currents
– Spectrum at different
currents
– Peak wavelength
– Threshold
– Operating current for
45 W optical output
Content
•
•
•
•
Setup
Status in October 2007
Status now
Characterization work
– Crystals
– Mirrors
– Diodes
• System improvement / outlook
– Crystal cooling
Improvements: new pump chambers
• More homogeneous
cooling at the crystal
surface ?
• Higher cooling
efficiency ?
• Less acoustic noise ?
Improvements: new pump chambers
Improvements: new pump chambers
old pump chamber
new pump chamber
2
heat transfer coefficient (W / m K)
25000
20000
15000
10000
5000
0
0
10
20
30
40
50
Position (mm)
• Calculated thermal lens for old chamber: 0.027 dpt/W
• Calculated thermal lens for new chamber: 0.025 dpt/W
Test setup
Improvements: new pump chambers
Summary
• System runs with lower output power and
more pump power than 6 month before
• Reason: probably lower doped crystals
• We have to take care that all incoming
components are well characterized and of the
same high quality
• Ideas on system improvement (pump
chambers) are going to be checked
Thank you for your attention !
Improvements: non-conventional cut
crystals
+ good birefringence
compensation with
quarz rotators
(adv. LIGO laser: output
power:  170 W cw, linear
polarized; depolarized
power: 1W)
- Additional
components inside
the resonator
(Absorption/thermal
effects/losses, spots)
- Sensitive adjustment
0°
5°
7°
Improvement: non-conventional cut
crystals
[111]-cut
[110]-cut
[100]-cut
1,0
birefringence parameter
• Reduction of
birefringence is possible
by use of crystals, which
are cut in [100]- or
[110]-direction instead
of [111]-direction1)
0,8
0,6
0,4
0,2
0,0
0
30
60
90
120
150
180
210
240
270
300
330
360
angular (degree)
• Birefringence depends
on the angle between
crystal-axis and
polarization-axis
1)
I. Shoji et al: Appl. Phys. Lett., Vol. 80, No. 17, 29 April 2002
Improvements: pump combiners
• 7x200µm input : 1
• up to 700 W input
power
• transfer efficiency >
93%
Source: ITF
Integrated fluorescence
RIN (unstabilized, locked laser)
0,01
8/07
3/08
1/2
RIN (1/Hz )
1E-3
1E-4
1E-5
1E-6
1E-7
1
10
100
1000
Frequency (Hz)
10000
100000
Spots on surfaces and coatings
• Spots on coatings
and optical
components knocked
out the system
several times
 Bring as few dust as
possible to the laser
table
 Check quality of
incoming
components
ca. 150 µm